Antinociceptive effects of vitexin in a mouse model of postoperative pain

Abstract

Vitexin, a C-glycosylated flavone present in several medicinal herbs, has showed various pharmacological activities including antinociception. The present study investigated the antinociceptive effects of vitexin in a mouse model of postoperative pain. This model was prepared by making a surgical incision on the right hindpaw and von Frey filament test was used to assess mechanical hyperalgesia. Isobolographical analysis method was used to examine the interaction between vitexin and acetaminophen. A reliable mechanical hyperalgesia was observed at 2 h post-surgery and lasted for 4 days. Acute vitexin administration (3-10 mg/kg, i.p.) dose-dependently relieved this hyperalgesia, which was also observed from 1 to 3 days post-surgery during repeated daily treatment. However, repeated vitexin administration prior to surgery had no preventive value. The 10 mg/kg vitexin-induced antinociception was blocked by the opioid receptor antagonist naltrexone or the GABAA receptor antagonist bicuculline. The doses of vitexin used did not significantly suppress the locomotor activity. In addition, the combination of vitexin and acetaminophen produced an infra-additive effect in postoperative pain. Together, though vitexin-acetaminophen combination may not be useful for treating postoperative pain, vitexin exerts behaviorally-specific antinociception against postoperative pain mediated through opioid receptors and GABAA receptors, suggesting that vitexin may be useful for the control of postoperative pain.

Figure 1. The time course of incisional surgery induced mechanical hyperalgesia in mice.

Control: control group that did not receive surgery. Model: model group that received surgery. Data were expressed as mean ± SEM (n = 12 per group), assessed by two-way ANOVA with repeated measures followed by Bonferroni post hoc analysis. *P < 0.001 compared to the corresponding data of control group. There was no differences in baseline mechanical paw withdrawal threshold (PWT) between control and model group pre-surgery (Pre). The incisional surgery induced mechanical hyperalgesia was observed at 2 h post-surgery and lasted for at least 4 days.

Figure 2. Effect of acute vitexin treatment on incision-induced mechanical hyperalgesia in mice.

Data were expressed as mean ± SEM (n = 12 per group), assessed by two-way ANOVA with repeated measures followed by Bonferroni post hoc analysis. Filled black symbols indicated data significantly different from the corresponding vehicle group. Dashed line indicated the average PWT of the left hind paw from the vehicle group (P < 0.05).

Figure 3. Effects of repeated vitexin treatment on incision-induced mechanical hyperalgesia in mice.

(A) Daily treatment with vitexin (3–10 mg/kg) improved incision-induced mechanical hyperalgesia in mice in a dose-dependent manner. Data were expressed as mean ± SEM (n = 10–12 per group), assessed by two-way ANOVA with repeated measures followed by Bonferroni post hoc analysis. Filled black symbols indicated data significantly different from the corresponding vehicle group (P < 0.05). (B) Daily treatment with 10 mg/kg vitexin has no accumulative analgesic effect on incision-induced mechanical hyperalgesia in mice. *P < 0.05 compared to the corresponding data of vehicle group. Filled black symbols indicated the PWTs prior to drug administration at 2, 3, 4 day after surgery during the period that mice received daily 10 mg/kg vitexin treatment, which was not different from the corresponding vehicle group.

Figure 4. Effects of pre-surgery repeated vitexin treatment on the incision-induced mechanical hyperalgesia in mice.

Data were expressed as mean ± SEM (n = 10 per group), assessed by two-way ANOVA with repeated measures followed by Bonferroni post hoc analysis. Repeated vitexin treatment for 6 days prior to incisional surgery did not alter the mechanical hyperalgesia in mice after surgery.

Figure 5. Effects of pretreatment with different receptor antagonists on the anti-hyperalgesic effects of vitexin (10 mg/kg) in mice receiving incisional surgery.

Data were expressed as mean ± SEM (n = 10–12 per group), assessed by two-way ANOVA with repeated measures followed by Bonferroni post hoc analysis. Filled black symbols indicated data significantly different from the corresponding vehicle group (P < 0.05).Both the opioid receptor antagonist naltrexone and the GABA_A receptor antagonist bicuculline but not the 5-HT_1A receptor antagonist WAY100635 completely blocked the anti-hyperalgesic effects of 10 mg/kg vitexin.

Figure 6. Effects of vitexin on the spontaneous locomotor activity in healthy mice.

Data were expressed as mean ± SEM (n = 12 per group), assessed by one-way ANOVA followed by Student–Newman–Keuls post hoc analysis. *P < 0.05 as compared to control group that did not receive vitexin treatment. Acute vitexin treatment at dose not more than 10 mg/kg did not significantly suppress the general locomotor activity, but increasing the dose to 20 mg/kg reduced the locomotor activity in mice.

Figure 7. Anti-hyperalgesic effect of vitexin and acetaminophen alone or in the drug mixture (vitexin-acetaminophen combinations in a fixed proportion of 1:1) in mice receiving incisional surgery.

Data were expressed as percentage of maximal possible effect (MPE) (mean ± SEM, n = 10–12 per group) and plotted as a function of drug dose; 100% MPE represented data from the pre-surgery baseline mechanical PWT.

Figure 8. Isobologram showing the anti-hyperalgesic interaction of vitexin (ED₅₀ = 1.95 mg/kg) and acetaminophen (ED₅₀ = 68.27 mg/kg) in the mouse model of incisional pain.

Abscissa scale: ED₅₀ value of acetaminophen; Ordinate scale: ED₅₀ value of vitexin (n = 10 per group). Horizontal and vertical bars indicate SEM. The oblique line between the x- and y-axes is the theoretical line of additivity. The dashed thin lines are the global 95% confidence boundaries, indicating the limits of the additive line. The point that represents ED₅₀ values (±SEM) of the drug mixture fell far above the limits of the additive line, suggesting a significant infra-additive interaction.